| 200 | ÷ | ( | 1 | + | r | ) | = | 9091 50 |
| 方程两边同时乘以: | ( | 1 | + | r | ) |
| 200 | = | 9091 50 | ( | 1 | + | r | ) |
| 200 | = | 9091 50 | × | 1 | + | 9091 50 | r |
| 200 | = | 9091 50 | + | 9091 50 | r |
| - | 9091 50 | r | = | 9091 50 | − | 200 |
| - | 9091 50 | r | = | - | 909 50 |
909 50 | = | 9091 50 | r |
9091 50 | r | = | 909 50 |
| r | = | 909 50 | ÷ | 9091 50 |
| = | 909 50 | × | 50 9091 |
| = | 909 | × | 1 9091 |
| r | = | 909 9091 |
| r | = | 0.099989 |